Federal Constitution of the United Mexican States (1824)

SECTION THIRD.

Article 25. The senate shall be composed of two senators from each
state, elected by an absolute majority of the legislature of each
state, one half of their number to be renewed every two years.

Article 26. The senators elected in the second place shall cease to hold
their places at the end of the two first years, and afterwards the most
ancient.

Article 27. When there occurs a vacancy in the senate on account of
death, resignation, or other cause, such vacancy shall be filled by the
legislature of the respective state, if such legislature be in session,
and if not, as soon as it may be in session.

Article 28. In order to be senator the same qualities are required,
which are prescribed in the preceding section for deputy, and moreover
to be thirty years at the time of the election.

Article 31. When the same individual is elected senator and deputy, he
shall prefer the election prior in point of time.

Article 32. The periodical election of senators shall take place in all
the states on the same day, which shall be the 1st of September next,
to the renewal of one-half of the senate.

Article 33. When the election of senators concludes, the different
legislatures shall forward a certificate of the same, through their
presidents to the council of government, in the usual form of acts of
election, and make known to the persons elected their appointment by
another instrument which shall serve as a credential of their election.
The president of the council of government shall dispose of these
certificates of election in the manner prescribed in the 18th article.